After hours of practice, his frustration was obvious when he still couldn't master the skill.

frustration 是名词，来自动词 frustrate（使受挫、挫败），表示"挫折感、沮丧的情绪"。这个词由拉丁词根 frustra（徒劳的）和后缀 -tion（表示状态或结果）组成，字面意思是"徒劳无功的状态"，即"挫败感"。